This invention relates generally to the field of engine cooling apparatus for work machines and, more a particularly, to a control system to control the speed and operation of an engine coolant circulation pump.
Prior art engine coolant systems are typically driven directly off the engine""s power train with a direct gear or belt drive arrangement wherein coolant flow is simply a function of engine speed. Since maximum exhaust temperature in an engine is typically reached near peak torque speed, the engine water pump capacity is usually designed and sized to provide the required engine coolant flow at that peak torque speed. Such an arrangement may result in excess coolant flow at higher engine speeds, which results in more heat rejection than necessary, and insufficient coolant flow at lower engine speeds. Such an arrangement also drives up the size of the cooling system, and excess power is wasted in pumping extra coolant flow at higher engine speeds because power consumption for an engine coolant pump typically increases with the cube of the pump speed. Still further, such prior art coolant systems create an unnecessary load upon the engine at start up, thereby creating an undesirable parasitic load and decreasing the cranking speed of the engine.
Another significant drawback in prior art systems is that the coolant system can cause overcooling of the engine in cold weather. In extremely cold ambient temperatures, even though engine thermostats bypass flow around the radiator, the engine still loses significant heat through the engine block and water lines wherein heat loss is a function of the coolant flow rate. At start up, during light load conditions, or at idle conditions, the coolant system can cool the engine to a temperature significantly below the desired minimum temperature or thermostat set point for the engine. As a result, engine reliability suffers when operating in an overcooled condition due to carbon build up on piston rings, valve stems and exhaust ports. Also, unburned fuel due to cold engine temperatures dilutes piston lubrication and depletes the oil base number due to the presence of fuel sulfur. Incomplete combustion of fuel also produces environmentally undesirable white smoke and slobber.
Therefore, it is desirable to control the performance of the engine coolant pump based upon the instantaneous heat dissipation requirements of the engine instead of controlling its performance as a function of engine speed. It is also desirable that the coolant system not be operational during the initial start up of the engine, and that the coolant pump operate at a minimum speed when the temperature of the engine falls below a predetermined threshold temperature to prevent overcooling. It is further desirable for the coolant pump speed to be proportionately variable when the coolant temperature is between certain predetermined minimum and maximum threshold temperatures thereby preventing insufficient or excessive cooling in the predetermined temperature threshold range.
Accordingly, the present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the present invention, a control system for controlling engine coolant flow in an engine is disclosed. The control system includes a first sensor positioned to sense the temperature of a first fluid in the engine and to output a signal indicative thereof, a second sensor positioned to sense the temperature of a second fluid in the engine and to output a signal indicative thereof, an electronic controller coupled with the first and second sensors for receiving signals therefrom, the controller being operable to receive a signal from the first sensor indicative of the temperature of the first fluid and to receive a signal from the second sensor indicative of the temperature of the second fluid, the controller being further operable to determine a desired engine coolant pump speed based upon the signals received from the first and second sensors, and the controller outputting a signal to the engine coolant pump to control the speed thereof, the output signal being indicative of the highest pump speed dictated by the signals received from the first and second sensors.
In another aspect of this invention, a method for controlling the speed of an engine coolant pump associated with an engine is disclosed. The method includes the steps of sensing the temperature of a first fluid associated with the engine, sensing the temperature of a second fluid associated with the engine, determining a first pump speed based upon the first sensed temperature, determining a second pump speed based upon the second sensed temperature, comparing the first pump speed determined in step of determining a first pump speed based upon the first sensed temperature with the second pump speed determined in the step of determining a second pump speed based upon the second sensed temperature, and setting the speed of the pump to the higher of the pump speeds determined in the step of determining a first pump speed based upon the first sensed temperature and the step of determining a second pump speed based upon the second sensed temperature.